水平管外壁液膜流动状态及其对传热的影响

FLOWING STATE OF LIQUID FILMS OVER HORIZONTAL TUBES AND ITS INFLUENCES ON HEAT-TRANSFER CHARACTERISTICS

采用智能化薄膜厚度测试仪对水平管外液膜流动状态进行了研究 ,得到液膜厚度的几率分布和平均厚度 .液膜的平均厚度不仅随液体负荷的增加而加大 ,而且与管外壁不同角度有关 ;液膜的波动状态受制于液体负荷与管径的共同影响 .定义了量纲 1波高 ,并通过实验数据回归得到量纲 1波高的经验关系式 .还进行了初步的传热实验 ,得到水平管外蒸发侧传热膜系数随量纲 1膜厚和量纲 1波高的变化 。

The film thickness distribution outside a horizontal test tube was measured with a film-thickness meter, to obtain the average thickness. The average film thickness increased with irrigation density of water. It was also relative to θ, and the waving intensity was controlled by both irrigation density and tube radius. Dimensionless wave amplitude was defined and correlated in terms of Reynolds number and tube diameter by regression of experimental data. Experiments of the evaporation heat-transfer coefficient on a horizontal-tube were conducted with various irrigation density, boiling point, temperature difference, heat flux and tube diameter. The influences of dimensionless film thickness and dimensionless wave amplitude on heat-transfer coefficients were obtained. These would provide a basis for further developing high efficiency heat-transfer process and evaporator.